This invention relates to a foreign matter inspection apparatus for detecting foreign matters, scratches, defects, contamination, and so forth (which will be altogether referred to as “foreign matters”) existing on a surface of an inspected object such as a glass substrate, a semiconductor wafer, or the like. More particularly, the invention relates to a foreign matter inspection apparatus for highly precisely correcting a position of an inspected object and detecting foreign matters with high accuracy and high sensitivity.
An apparatus for detecting the existence of foreign matters existing on a surface of an inspected object such as a glass substrate and a semiconductor wafer by irradiating an optical beam such as a laser beam to the surface of the inspected object and detecting a reflected or scattered beam occurring from the surface is known as a foreign matter inspection apparatus for (refer to JP-A-5-47901). In this foreign matter inspection apparatus, an image signal is generated from the intensity of reflected or scattered beams detected from each chip when a large number of IC chips originally having the same pattern are formed on a semiconductor wafer, and this image signal is compared with an image signal obtained from an adjacent chip or with an image signal from an approved chip prepared in advance. A matter on the surface of the semiconductor wafer is judged as the foreign matter when a difference between these image signals is greater than a threshold value.
When the image signal described above is collected, chips juxtaposed in a transverse direction on the surface of the inspection object must be put in parallel with a scanning direction of the optical beam. Because the difference signal is collected through comparison with the adjacent chips, variance occurs in the difference signal owing to the kind of the pattern contained in the detection region or the difference of the density such as wiring layout inside the chips and scribe lines among the chips and the inspection result is adversely affected.
As an alignment method for arranging parallel the inspected object, a method has been employed that collects coordinates (X, Y) of two points inside the inspected object with alignment marks formed inside the chips on the surface of the inspected object as the reference, and moves an inspection stage for correction on the basis of the deviation amount of the inspected object calculated from the coordinates.
Detection of foreign matters having smaller sizes has become necessary in recent years with the increase of an integration density and further miniaturization of semiconductors. To suppress variance of the error signal and to improve detection accuracy and reproducibility, higher alignment accuracy has been required. Nonetheless, alignment has become more and more difficult owing to miniaturization of the alignment marks and the drop of contrast resulting from the manufacturing process.
A method that prepares a projection waveform of a reticle substrate as reference image data (hereinafter called “template”) and determines an error amount from pattern matching with a projection waveform obtained in practice from a position adjustment rectile substrate is known as an alignment method of an inspection position (refer to JP-A-10-106941, for example).
As for pattern matching methods, a method that detects an image signal from an inspection object, extracts a predetermined feature amount from the image signal to form an abstracted pattern and executes pattern matching between this abstracted pattern and an abstracted pattern obtained from the reference image (template) is known (refer to JP-A-11-340115, for example).
When a position error of a pattern wafer put on a movable stage is automatically aligned in an inspection apparatus for inspecting a pattern wafer, chips are aligned accurately and precisely on the pattern wafer. To inspect the pattern wafers, the wafers must be aligned in X and Y directions of a stage. However, immediately after the wafers are transferred to the stage, the wafers are not correctly aligned in the X and Y directions and must be positioned in the X and Y directions by rotating the stage.
To align the pattern wafers, a plurality of correction marks is formed, a CCD camera is used to image the positions of the correction marks and these positions are measured by a pattern matching process. A rotation angle of the stage to be corrected is then calculated from a plurality of points.
Generally, imaging is made in alignment by using two kinds of magnification cameras. To improve accuracy of the correction angle to be calculated, the positions of the correction marks must be detected with high accuracy. However, the imaging visual field of the magnification camera is narrow and the probability of covering the correction marks by a single imaging operation becomes low. For this reason, a system has been employed that detects a rough position by a low magnification camera and then accuracy is improved by switching the camera to a high magnification camera.
However, this system involves the problem that alignment needs a long time. To improve inspection through-put, it would be conceivable to derive an optimal magnification ratio from alignment accuracy and a positioning error of the stage at the time of transfer and to conduct alignment at a single magnification. JP-A-11-220006 can be cited as one of the references relating to this technology.
In alignment at a single magnification, however, three or more marks of correction marks for calculating a correction angle for detecting a recognition error of other pattern as a correction mark and confirmation marks for confirming alignment accuracy are necessary. When the wafer is transferred to the stage, the center of the wafer deviates from the center of the stage and the coordinate position of the correction mark for confirmation deviates, too. Therefore, the coordinate position of the confirmation mark must be detected before correction. However, the movement of the stage and the pattern matching processing become necessary and the processing time gets elongated. The coordinates of the confirmation mark must be therefore calculated in advance from the coordinates of the correction mark detected.
The technology described in JP-A-10-106941 executes a collective correction processing of a position error amount between going and returning strokes when an inspected object is scanned in going and returning directions by optical beams. This technology cannot be applied to a foreign matter inspection apparatus that requires high precision alignment of individual inspected objects. Since the technology is directed to a reticle substrate produced as a jig that is dedicated to the adjustment of the positioning error, it does not take into consideration those adverse influences which may be exerted on various kinds of thin films produced in the manufacturing process of semiconductor devices such as semiconductor films, metal films, insulating films, and so forth, and problems of the recognition failure due to the drop of contrast of the alignment marks and the matching mistake with other alignment marks are unavoidable.
It has been customary in the past for an operator to select an alignment mark while watching an observation screen of an inspected object and to register the image data as a template. When an inspection process of semiconductor device products is a manufacturing process which invites the drop of contrast, however, it is difficult to observe the alignment marks with eye. Therefore, the operator empirically repeats selection of the alignment marks but a long time is necessary to set a complicated evaluation condition of the template and a collection work. Furthermore, when an error of an angle (θ) occurs in the inspected object, it is difficult to use the template as such and correction of the angle is necessary. The error of the correction process results in the drop and variance of alignment accuracy.